The French chemist Antoine Laurent Lavoisier (1743-1794) was the founder of the modern science of chemistry and the author of the oxygen theory of combustion.
Antoine Laurent Lavoisier
Antoine Laurent Lavoisier was born in Paris on Aug. 26, 1743, the son of an attorney at the Parlement of Paris. Lavoisier began his schooling at the Collège Mazarin in Paris at the age of 11. In his last two years (1760-1761) at the college his scientific interests were aroused. In the philosophy class he came under the tutelage of Abbé Nicolas Louis de Lacaille, a distinguished mathematician and observational astronomer who imbued the young Lavoisier with an interest in meteorological observation, an enthusiasm which never left him.
Lavoisier entered the school of law, where he received a bachelor's degree in 1763 and a licentiate in 1764. However, he continued his scientific education in his spare time. In 1764 he read his first paper to the French Academy of Sciences, on the chemical and physical properties of gypsum (hydrated calcium sulfate), and in 1766 he was awarded a gold medal by the King for an essay on the problems of urban street lighting.
In 1768 Lavoisier received a provisional appointment to the Academy of Sciences. About the same time he bought a share in the Tax Farm, a financial company which advanced the estimated tax revenue to the royal government in return for the right to collect the taxes. It was to prove a fateful step. Lavoisier consolidated his social and economic position when, in 1771, he married Marie Anne Pierrette Paulze, the 14-year-old daughter of a senior member of the Tax Farm. She was to play an important part in Lavoisier's scientific career, translating English chemical works into French for him, assisting in the laboratory, and drawing diagrams for his scientific works.
For 3 years following his entry into the Tax Farm, Lavoisier's scientific activity diminished somewhat, for much of his time was taken up with official Tax Farm business. He did, however, present one important memoir to the Academy of Sciences during this period, on the supposed conversion of water into earth by evaporation. By a very precise quantitative experiment Lavoisier showed that the "earthy" sediment produced after long-continued reflux heating of water in a glass vessel was not due to a conversion of the water into earth but rather to the gradual disintegration of the inside of the glass vessel produced by the boiling water.
Oxygen Theory of Combustion
During the summer and fall of 1772 Lavoisier turned his attention to the phenomenon of combustion, the topic on which he was to make his most significant contribution to science. He reported the results of his first experiments on combustion in a note to the academy on October 20 in which he reported that when phosphorus burned it combined with a large quantity of air to produce acid spirit of phosphorus (phosphoric acid) and that the phosphorus increased in weight on burning. In a second sealed note deposited with the academy a few weeks later (November 1) Lavoisier extended his observations and conclusions to the burning of sulfur and went on to add that "what is observed in the combustion of sulfur and phosphorus may well take place in the case of all substances that gain in weight by combustion and calcination: and I am persuaded that the increase in weight of metallic calces is due to the same cause."
During 1773 Lavoisier determined to review thoroughly the literature on air, particularly "fixed air," and to repeat many of the experiments of other workers in the field. He published an account of this review in 1774 in a book entitled Opuscules physiques et chimiques (Physical and Chemical Essays). In the course of this review he made his first full study of the work of Joseph Black, the Scottish chemist who had carried out a series of classic quantitative experiments on the mild and caustic alkalies. Black had shown that the difference between a mild alkali, for example, chalk (CaCO3), and the caustic form, for example, quicklime (CaO), lay in the fact that the former contained "fixed air," not common air fixed in the chalk, but a distinct chemical species, carbon dioxide (CO2), which was a constituent of the atmosphere. Lavoisier recognized that Black's fixed air was identical with the air evolved when metal calces were reduced with the charcoal and even suggested that the air which combined with metals on calcination and increased the weight might be Black's fixed air, that is, CO2.
In the spring of 1774 Lavoisier carried out experiments on the calcination of tin and lead in sealed vessels which conclusively confirmed that the increase in weight of metals on calcination was due to combination with air. But was it combination with common atmospheric air or with only a part of atmospheric air? In October the English chemist Joseph Priestley visited Paris, where he met Lavoisier and told him of the air which he had produced by heating the red calx of mercury with a burning glass and which had supported combustion with extreme vigor. Priestley at this time was unsure of the nature of this gas, but he felt that it was an especially pure form of common air. Lavoisier carried out his own researches on this peculiar substance. The result was his famous memoir "On the Nature of the Principle Which Combines with Metals during Their Calcination and Increases Their Weight," read to the academy on April 26, 1775 (commonly referred to as the Easter Memoir). In the original memoir Lavoisier showed that the mercury calx was a true metallic calx in that it could be reduced with charcoal, giving off Black's fixed air in the process. When reduced without charcoal, it gave off an air which supported respiration and combustion in an enhanced way. He concluded that this was just a pure form of common air, and that it was the air itself "undivided, without alteration, without decomposition" which combined with metals on calcination.
After returning from Paris, Priestley took up once again his investigation of the air from mercury calx. His results now showed that this air was not just an especially pure form of common air but was "five or six times better than common air, for the purpose of respiration, inflammation, and … every other use of common air." He called the air dephlogisticated air, as he thought it was common air deprived of its phlogiston. Since it was therefore in a state to absorb a much greater quantity of phlogiston given off by burning bodies and respiring animals, the greatly enhanced combustion of substances and the greater ease of breathing in this air were explained.
The "official" version of Lavoisier's Easter Memoir did not appear until 1778. In the intervening period Lavoisier had ample time to repeat some of Priestley's latest experiments and perform some new ones of his own. In addition to studying Priestley's dephlogisticated air, he studied more thoroughly the residual air after metals had been calcined. He showed that this residual air supported neither combustion nor respiration and that approximately five volumes of this air added to one volume of the dephlogisticated air gave common atmospheric air. Common air was then a mixture of two distinct chemical species with quite different properties. Thus when the revised version of the Easter Memoir was published in 1778, Lavoisier no longer stated that the principle which combined with metals on calcination was just common air but "nothing else than the healthiest and purest part of the air" or the "eminently respirable part of the air." In the following year Lavoisier coined the name oxygen for this constituent of the air, from the Greek words meaning "acid former." He was struck by the fact that the combustion products of such nonmetals as sulfur, phosphorus, charcoal, and nitrogen were acidic. He held that all acids contained oxygen and that oxygen was therefore the acidifying principle.
Lavoisier's new theory of combustion was virtually complete. He was now ready to mount a wholesale attack on the current phlogiston theory.
Lavoisier the Public Servant
Lavoisier's researches on combustion were carried out in the midst of a very busy schedule of public and private duties, especially in connection with the Tax Farm. There were also innumerable reports for and committees of the Academy of Sciences to investigate specific problems on order of the royal government. Lavoisier, whose organizing skills were outstanding, frequently landed the task of writing up such official reports. In 1775 he was made one of four commissioners of gunpowder appointed to replace a private company, similar to the Tax Farm, which had proved unsatisfactory in supplying France with its munitions requirements. As a result of his efforts, both the quantity and quality of French gunpowder greatly improved, and it became a source of revenue for the government. His appointment to the Gunpowder Commission brought one great benefit to Lavoisier's scientific career as well. As a commissioner, he enjoyed both a house and a laboratory in the Royal Arsenal. Here he lived and worked between 1775 and 1792.
Consolidation of the New Theory
Lavoisier's chemical research between 1772 and 1778 was largely concerned with developing his own new theory of combustion. In 1783 he read to the academy his famous paper entitled "Reflections of Phlogiston," a full-scale attack on the current phlogiston theory of combustion. That year Lavoisier also began a series of experiments on the composition of water which were to prove an important capstone to his combustion theory and win many converts to it. Many investigators had been experimenting with the combination of inflammable air (hydrogen) with dephlogisticated air (oxygen) by electrically sparking mixtures of the gases. All of the researchers noted the production of water, but all interpreted the reaction in varying ways within the framework of the phlogiston theory. In cooperation with mathematician Pierre Simon de Laplace, Lavoisier synthesized water by burning jets of hydrogen and oxygen in a bell jar over mercury. The quantitative results were good enough to support the contention that water was not an element, as had been thought for over 2,000 years, but a compound of two gases, hydrogen and oxygen.
Lavoisier, together with L. B. Guyton de Morveau, Claude Louis Berthollet, and Antoine François de Fourcroy, submitted a new program for the reforms of chemical nomenclature to the academy in 1787, for there was virtually no rational system of chemical nomenclature at this time. The new system was tied inextricably to Lavoisier's new oxygen theory of chemistry. The Aristotelian elements of earth, air, fire, and water were discarded, and instead some 55 substances which could not be decomposed into simpler substances by any known chemical means were provisionally listed as elements. The elements included light; caloric (matter of heat); the principles of oxygen, hydrogen, and azote (nitrogen); carbon; sulfur; phosphorus; the yet unknown "radicals" of muriatic acid (hydrochloric acid), boracic acid, and "fluoric" acid; 17 metals; 5 earths (mainly oxides of yet unknown metals such as magnesia, barite, and strontia); three alkalies (potash, soda, and ammonia); and the "radicals" of 19 organic acids. The acids, regarded in the new system as compounds of various elements with oxygen, were given names which indicated the element involved together with the degree of oxygenation of that element, for example sulfuric and sulfurous acids, phosphoric and phosphorus acids, nitric and nitrous acids, the "ic" termination indicating acids with a higher proportion of oxygen than those with the "ous" ending. Similarly, salts of the "ic" acids were given the terminal letters "ate," as in copper sulfate, whereas the salts of the"ous" acids terminated with the suffix "ite," as in copper sulfite. The total effect of the new nomenclature can be gauged by comparing the new name "copper sulfate" with the old term "vitriol of Venus."
Lavoisier employed the new nomenclature in his Elements of Chemistry, published in 1789. This work represents the synthesis of Lavoisier's contribution to chemistry and can be considered the first modern text-book on the subject. The core of the Elements of Chemistry was the oxygen theory, and the work became a most effective vehicle for the transmission of the new doctrines. It remains a classic in the history of science.
His Physiological Studies
The relationship between combustion and respiration had long been recognized from the essential role which air played in both processes. Lavoisier was almost obliged, therefore, to extend his new theory of combustion to include the area of respiration physiology. His first memoirs on this topic were read to the Academy of Sciences in 1777, but his most significant contribution to this field was made in the winter of 1782/1783 in association with Laplace. The result of this work was published in a famous memoir, "On Heat." Lavoisier and Laplace designed an ice calorimeter apparatus for measuring the amount of heat given off during combustion or respiration. By measuring the quantity of carbon dioxide and heat produced by confining a live guinea pig in this apparatus, and by comparing the amount of heat produced when sufficient carbon was burned in the ice calorimeter to produce the same amount of carbon dioxide as that which the guinea pig exhaled, they concluded that respiration was in fact a slow combustion process. This continuous slow combustion, which they supposed took place in the lungs, enabled the living animal to maintain its body temperature above that of its surroundings, thus accounting for the puzzling phenomenon of animal heat.
Lavoisier continued these respiration experiments in 1789-1790 in cooperation with Armand Seguin. They designed an ambitious set of experiments to study the whole process of body metabolism and respiration using Seguin as a human guinea pig in the experiments. Their work was only partially completed and published because of the disruption of the Revolution; but Lavoisier's pioneering work in this field served to inspire similar research on physiological processes for generations to come.
As the Revolution gained momentum from 1789 on, Lavoisier's world inexorably collapsed around him. Attacks mounted on the Tax Farm, and it was eventually suppressed in 1791. In 1792 Lavoisier was forced to resign from his post on the Gunpowder Commission and to move from his house and laboratory at the Royal Arsenal. On Aug. 8, 1793, all the learned societies, including the Academy of Sciences, were suppressed.
It is difficult to assess Lavoisier's own attitude to the political turmoil. Like so many intellectual liberals, he felt that the Old Regime could be reformed from the inside if only reason and moderation prevailed. Characteristically, one of his last major works was a proposal to the National Convention for the reform of French education. He tried to remain aloof from the political cockpit, no doubt fearful and uncomprehending of the violence he saw therein. However, on Nov. 24, 1793, the arrest of all the former tax gatherers was ordered. They were formally brought to trial on May 8, 1794, and convicted with summary justice of having plundered the people and the treasury of France, of having adulterated the nation's tobacco with water, and of having supplied the enemies of France with huge sums of money from the national treasury. Lavoisier, along with 27 of his former colleagues, was guillotined on the same day.
Further Reading on Antoine Laurent Lavoisier
The best source for a study of Lavoisier is the translation of his Traité elémentaire de chimie, printed as Elements of Chemistry with an introduction by Douglas McKie, in 1965. The most comprehensive biography of Lavoisier in English is Douglas McKie, Antoine Lavoisier: Scientist, Economist, Social Reformer (1952). Henry Guerlac, Lavoisier: The Crucial Years (1961), deals with the factors which led Lavoisier to study the combustion problem. See also Sidney J. French, Torch and Crucible: The Life and Death of Antoine Lavoisier (1941). James Bryant Conant, ed., The Overthrow of the Phlogiston Theory (1955), is a clear and valuable study of this aspect of the chemical revolution.